SOQuartz Software Releases
pgwipeout's Quartz CI
pgwipeout's Quartz CI includes a Debian installer image for the SOQuartz, with the CM4 I/O board as the base board. Assuming your target device is /dev/sdb, you can flash it with:
sudo -i; xzcat /path/to/rk3566-soquartz-cm4.dtb.img.xz > /dev/sdb
You will need 3.3V UART at 1.5 mbauds (1500000) to access the interface.